Seismometers capture the sounds of tremors and icequakes from deep inside glaciers and speed them up for our ears to hear.

Glaciers are not simply the enormous, placid rafts of ice they appear to be. They're active on the inside, with water flowing through a complex network of fractures and melt pockets that change all the time. We can't see it. But, according to new research, we can hear it.

Scientists stuck some seismometers into Gorner Glacier in the Swiss Alps. As lake water flowed through the glacier, the seismometers picked up tiny tremors and the sounds of icequakes at the glacier's base.

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The research team, led by David Heeszel of the Scripps Institution of Oceanography, deployed eight seismometers through boreholes in the ice, one of which was buried 120 meters below the surface. Then the team sped up the seismogram 250 times so that humans could hear the rumblings, according to Motherboard.

The way liquid water flows through a glacier isn't well understood, but it's important for monitoring the risk of glacial lake outburst floods. Those happen when a glacier-formed dam or moraine dam bursts. (A moraine is like a glacier's crumbs—the rocks and debris left behind as it recedes.)

Glaciers shrink as they melt, and sometimes their meltwater forms unstable lakes. As more of the glacier melts and snowmelt fill the lakes, these natural glacier or moraine dams can weaken and fail. The resulting glacier floods can be deadly—and glacial lake outburst floods could become more common as the Earth warms.

Glacial outburst floods are hard to predict because water can follow any number of pathways over, under or through a glacier. Watching the surface won't yield any clues, because all we see is a peaceful hunk of ice. But listening to them might help: This glacier humming could be used as an early warning sign.